@Dave Chennault I do not have experience using flow but I think in this case the authentication bearer token is not passed along with the headers. I have an old endpoint of the classic studio that is still running and the steps to use the endpoint through REST can be obtained by clicking the REQUEST/RESPONSE link of the endpoint page from the studio.
I used postman to call the endpoint using the authorization method mentioned i.e Bearer token with the key mentioned in the endpoints page. Header value of Content-Type:application/json
I hope this helps!!
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